1. Field of the Invention
The present invention relates to a controlling device for an internal combustion engine, and a method of estimating an open degree of an intake air flow controlling valve of the internal combustion engine.
2. Description of Related Art
An internal combustion engine has a combustion chamber and an intake air flow controlling valve. The valve generates vortex flow of air-fuel mixture in the combustion chamber, and is arranged at a downstream side of a throttle valve. The vortex flow may be a tumble flow or swirl flow, for example.
The internal combustion engine further has a controlling device to control ignition timing and fuel amount based on an open degree of the valve. Therefore, it is important to accurately detect the open degree of the valve so as to improve drive performance.
JP-A-62-223440 or JP-A-H11-190218 discloses a method of detecting an open degree of an intake air flow controlling valve. In the method, only full open and full close of the valve are detected by using a limit switch, or an actual open degree of the valve is linearly monitored by using a linear sensor.
However, when the valve has a mid-opening positioned between the full open and the full close, the method of JP-A-62-223440 fails to detect the mid-opening. In this case, drive performance may not be improved. Although the mid-opening may be able to be estimated, if an estimated value has a large error relative to an actual value, drive performance is lowered. Therefore, accuracy for estimating the open degree is required to be increased.
The method of JP-A-H11-190218 enables an engine to be controlled by using a signal output from the linear sensor. However, cost of the linear sensor is higher than that of the limit switch.